Psychostimulant abuse and vulnerability to dependence (addiction) and relapse during abstinence linger as major public health problems in the United States and effective, safe pharmacotherapeutic approaches are needed. The 5-HT2CR receptor (5-HT2CR) has been identified as an important mediator of the behavioral effects of psychostimulants and selective 5-HT2CR agonists have shown efficacy in suppression of the discriminative stimulus effects of stimulants as well as drug-taking and drug-seeking in self-administration models. Thus, strategies to maximize signaling through the 5-HT2CR may prove therapeutically useful to inhibit relapse in stimulant abusers. The recent discovery that the 3rd intracellular loop of the 5-HT2CR binds protein phosphatase and tensin homologue deleted on chromosome 10 to control activation states of the receptor provides a new medication development opportunity. The 5- HT2CR:PTEN complex is disrupted by a small peptide fragment of the 5-HT2CR which evokes 5- HT2CR agonist-like properties in vivo with a limited side effect profile, suggesting that either brain-penetrant peptides or small molecules that inhibit the 5-HT2CR:PTEN association will be a novel method to enhance 5-HT2CR function. In the present proposal, submitted in response to RFA-DA-10-018, we will examine the 5-HT2CR:PTEN association as a novel pharmacological target using a multidisciplinary approach involving chemistry, molecular modeling, live cell assays in vitro and preclinical models of addiction in vivo. We will design and synthesize new peptide and peptidomimetic inhibitors of the 5-HT2CR:PTEN interaction based on the modeled peptide interface between the 5-HT2CR and PTEN, and convert these into small molecules optimized for high activity and drug-like properties. These novel inhibitors will be evaluated in live cell assays for their efficacy to disrupt the 5-HT2CR:PTEN complex and enhance signaling through the 5-HT2CR. The potency, efficacy and selectivity of optimized inhibitors of the 5- HT2CR:PTEN interaction will be assessed in vivo in using rat drug discrimination models. The most promising candidates will be evaluated in cocaine self-administration and reinstatement assays. The proposed studies will provide novel peptides, small molecules and cellular assays to probe the neurobiological function of the 5-HT2CR macromolecular complex and potentially discover novel therapeutic agents for the treatment of psychostimulant addiction in humans. PUBLIC HEALTH RELEVANCE: New, effective and accessible modalities for the treatment of stimulant addiction are needed to alleviate the chronic, psychological and physical burdens of substance abuse disorders. Through a multidisciplinary project including chemistry, cell biology and behavior, we will develop new peptides and drugs to explore and validate a new brain target in addiction. These compounds and the new assays developed here will allow us to probe the biology of the brain to create new ways to enhance abstinence in stimulant-dependent individuals.